Field of the Invention
The present invention pertains to polyurethane and polyisocyanurate foams and methods for the preparation thereof. More particularly, the invention relates to rigid, polyurethane and polyisocyanurate foams and methods for their preparation, which foams are characterized by a fine uniform cell structure and little or no foam collapse. The foams are produced with an organic polyisocyanate and a polyol premix composition which comprises a combination of a blowing agent, which is preferably a hydrohaloolefin, a polyol, a silicone surfactant, and an amine catalyst.
Description of the Related Art
The class of foams known as low density, rigid polyurethane or polyisocyanurate foams has utility in a wide variety of insulation applications including roofing systems, building panels, building envelope insulation, refrigerators and freezers. A critical factor in the large-scale commercial acceptance of rigid polyurethane foams has been their ability to provide a good balance of properties. Rigid polyurethane and polyisocyanurate foams are known to provide outstanding thermal insulation, excellent fire resistance properties, and superior structural properties at reasonably low densities. The foam industry has historically used liquid fluorocarbon blowing agents because of their ease of use in processing conditions. Fluorocarbons not only act as blowing agents by virtue of their volatility, but also are encapsulated or entrained in the closed cell structure of the rigid foam and are the major contributor to the low thermal conductivity properties of the rigid urethane foams. The use of a fluorocarbon as the preferred commercial expansion or blowing agent in insulating foam applications is based in part on the resulting k-factor associated with the foam produced. The k-factor is defined as the rate of transfer of heat energy by conduction through one square foot of one-inch thick homogenous material in one hour where there is a difference of one degree Fahrenheit perpendicularly across the two surfaces of the material. Since the utility of closed-cell polyurethane-type foams is based, in part, on their thermal insulation properties, it would be advantageous to identify materials that produce lower k-factor foams.
It is known in the art to produce rigid polyurethane and polyisocyanurate foams by reacting a polyisocyanate with a polyol in the presence of a blowing agent, a catalyst, a surfactant, and optionally other ingredients. Blowing agents include hydrocarbons, fluorocarbons, chlorocarbons, fluorochlorocarbons, halogenated hydrocarbons, ethers, esters, aldehydes, ketones, or CO2 generating materials. Heat generated when the polyisocyanate reacts with the polyol volatilizes the blowing agent contained in the liquid mixture, thereby forming bubbles therein. As the polymerization reaction proceeds, the liquid mixture becomes a cellular solid, entrapping the blowing agent in the foam's cells. If a surfactant is not used in the foaming composition, the bubbles simply pass through the liquid mixture without forming a foam or forming a foam with large, irregular cells rendering it not useful. Preferred blowing agents have low global warming potential. Among these are hydrohaloolefins including hydrohaloolefins (HFOS) of which trans-1,3,3,3-tetrafluoropropene (HFO-1234ze) is of particular interest and hydrochlorofluoroolefins (HFCOs) of which 1-chloro-3,3,3-trifluoropropene (HFCO-1233zd) is of particular interest. Processes for the manufacture of 1,3,3,3-tetrafluoropropene are disclosed in U.S. Pat. Nos. 7,230,146 and 7,189,884. Processes for the manufacture of 1-chloro-3,3,3-trifluoropropene are disclosed in U.S. Pat. Nos. 6,844,475 and 6,403,847.
It is convenient in many applications to provide the components for polyurethane or polyisocyanurate foams in pre-blended formulations. Most typically, the foam formulation is pre-blended into two components. The polyisocyanate and optional isocyanate compatible raw materials comprise the first component, commonly referred to as the “A” component. A polyol or mixture of polyols, surfactant, catalyst, blowing agent, and other isocyanate reactive and non-reactive components comprise the second component, commonly referred to as the “B” component. Accordingly, polyurethane or polyisocyanurate foams are readily prepared by bringing together the A and B side components either by hand mix for small preparations and, preferably, machine mix techniques to form blocks, slabs, laminates, pour-in-place panels and other items, spray applied foams, froths, and the like. Optionally, other ingredients such as fire retardants, colorants, auxiliary blowing agents, and other polyols can be added to the mixing head or reaction site. Most conveniently, however, they are all incorporated into one B component.
A shortcoming of two-component systems, especially those using certain hydrohaloolefins, including HFO-1234ze and HFCO-1233zd is the shelf-life of the B-side composition. Normally when a foam is produced by bringing together the A and B side components, a good foam is obtained. However, if the polyol premix composition is aged, prior to treatment with the polyisocyanate, the foams are of lower quality and may even collapse during the formation of the foam.
It has now been found that the origin of the problem is the reaction of certain amine catalysts with certain hydrohaloolefins including HFO-1234ze and HFCO-1233zd, resulting in partial decomposition of the blowing agent. It has been found that, subsequent to the decomposition of the blowing agent, the molecular weight of the polymeric silicone surfactants, if present, is detrimentally altered, leading to poor foam structure.
While it is possible to solve the problem by separating the blowing agent, surfactant, and catalyst, for example by adding the blowing agent, amine catalyst, or surfactant to the polyisocyanate, (“A” component) or by introducing the blowing agent, amine catalyst, or surfactant using a separate stream from the “A” or “B” component, a preferred solution is one that does not require reformulation or a change in the way the foams are made.
It has now been found that sterically hindered amines have lower reactivity toward certain blowing agents, such as hydrohaloolefins including trans HFO-1234ze and HFCO-1233zd, such that good quality foams can be produced even if the polyol blend has been aged.